It is known that many aquatic invertebrates such as crustaceans go through a cycle of moulting, in which an old hard shell is shed and a new larger soft shell is grown. Depending on the stage of the moulting process, a crustacean's internal body, i.e., the “meat” portion of a lobster for example, may occupy a reduced part of the internal volume of the new shell as the internal body grows to occupy the new, larger shell. The internal structure of a crustacean, including its organs, meat and muscle, is undersized in proportion to its new shell after moulting. In order to “fill out” a new, oversized shell after moulting, a crustacean takes on and retains water within its internal structure. As a result, inter-moult crustaceans (hard shell) generally produce high meat yields, while post-moult (soft shell) crustaceans generally produce lower meat yields.
Seafood is often an expensive food product for which a consumer might consider paying a premium. In return, the consumer expects to receive a high quality product that reflects the price paid. For example, consumers will often pay a premium for larger crustaceans, in terms of weight and/or size, and the consumer will generally expect the size of the crustacean to correspond to the amount of meat yielded by the crustacean. However, due to variances in moult stage, a larger post-moult crustacean might not yield any more meat than a smaller pre-moult or inter-moult crustacean. Beyond meat yield or “meatedness”, the moult state of a crustacean can also be indicative of health, enabling a seafood processor to assess anticipated mortality rates during storage and/or shipment of crustaceans.
Inter-moult crustaceans can often be identified by their shell hardness. However, this measure is unreliable as a means to determine meat yields and is difficult to implement as a non-invasive measure on a production line. Other attempts at sensing systems employing ultrasound or x-ray scanning systems have proven difficult to implement and have failed to accurately distinguish between different shell hardnesses and/or different meat yields.
Other methods used in determining moult stage include blood protein analysis and pleopod staging. Both of these methods are invasive, and are typically applied only to a subsample of a crustacean harvest or shipment. These methods also require specialised training to properly interpret results that would accurately determine moult stage or meat yield.
There are also other physical attributes of individual crustaceans that are often measured or otherwise determined manually. These include carapace length for lobster, a measurement which is often used for determining the size of a lobster and which is also used within harvesting regulations for minimum allowable legal sized lobster (for example, 80-85 mm carapace length depending on the fishing district), cracked or damaged exoskeletons, missing or broken legs, gender, and shell morphometrics such as various claw, body and/or tail measurements.